Programmable logic devices (PLDs) are a well-known type of integrated circuit (IC) that can be programmed to perform specified logic functions. One type of PLD, the field programmable gate array (FPGA), typically includes an array of programmable tiles. These programmable tiles can include, for example, input/output blocks (IOBs), configurable logic blocks (CLBs), dedicated random access memory blocks (BRAM), multipliers, digital signal processing blocks (DSPs), processors, clock managers, delay lock loops (DLLs), and so forth.
Each programmable tile typically includes both programmable interconnect and programmable logic. The programmable interconnect typically includes a large number of interconnect lines of varying lengths interconnected by programmable interconnect points (PIPs). The programmable logic implements the logic of a user design using programmable elements that can include, for example, function generators, registers, arithmetic logic, and so forth.
The programmable interconnect and programmable logic are typically programmed by loading a stream of configuration data (bitstream) into internal configuration memory cells that define how the programmable elements are configured. The configuration data can be read from memory (e.g., from an external PROM) or written into the FPGA by an external device. The collective states of the individual memory cells then determine the function of the FPGA.
Some applications require that system components have a degree of isolation among themselves. Within some military applications, for example, circuit designs must conform to a standard referred to as Multiple Independent Levels of Security (MILS). One aspect of MILS is the partitioning of a system so that the failure or corruption of any single partition will not corrupt any other partition of the system or cause a failure in such other partition(s). With respect to circuits, for example, MILS requires a degree of electrical isolation between different partitions of a system. Different partitions of a cryptographic application, for example, often must be isolated from one another.